From a Business standpoint the removal of PS3 back-compat. makes much sense, because of what we are reading here: many people still play and are willing to buy a PS2.
Also, we must not forget that there are diferent markets all over the world. Many parents buy PS2 for their yonger kids, there is a large variety of party and junior games available. People with less income started gaming more often due to the lower console and game prices. In South America, for ex., the console sells very well.
All in all, its wonderfull to see an older console still having such support, i own a PS3 and a Xbox360, but i still buy PS2 games. It makes me happy the PS2 was the greatest gaming investment i have ever made, in terms of bang-for-the-buck ofc.
P.S.- talking about different markets and consumer needs, a fun\sad fact: Eastern Europe skipped the NES generation due to the Iron Curtain, but still gamers found a way, in pirate systems.
Behold: The Ending-Man!